1. Field of the Invention
This invention relates to preparing documents for printing. In particular, this invention relates to a method for proofing imposed documents, for example books, magazines and brochures, on a proofing medium.
2. Description of the Prior Art
Generally, modern production techniques for documents such as books, magazines and brochures, can be split into three major stages:
1. Prepress. In the prepress stage of production, media are prepared for a printing device. The output of this stage is an imaged film, plate, cylinder or, in the case of digital printing presses, digital data. One of the steps in the prepress stage is imposition. This step ensures that each page of the document is placed on the proper printing sheet in the correct orientation. PA1 2. Printing. During this stage of production the information produced by the prepress system is duplicated on sheets of output medium using a press, a digital printing system, or some other duplicator of printed material. PA1 3. Finishing. In this stage the printed sheets of output medium are folded, assembled and cut to form the final documents.
Since stages 2 and 3 generally are used for high volume work, the fixed cost of stage 1 and the set up of printing and finishing is very high compared to the variable marginal cost of printing one document. Errors discovered only in the printing or finishing stages tend to be very expensive. Professional printers thus want to see a simulation of the result of stages 2 and 3 before actually performing these processes. They also need to be able to provide proofs that give customers a clear impression of how the actual printed document will look.
Imposition usually is carried out on a computer, using an imposition software program which takes the individual pages of a document and lays the pages out on large sheets ("print sheets"), several pages to a sheet, so that after printing, the print sheets can be folded and cut to generate one or more subsets ("sections") of the document which are then combined to form a complete document. Typical prior art imposition programs generate printing data comprising at least one computer file containing information about the position of the pages on sheets of output medium ("print sheets") as well as the content of these pages. Typically, the printing data might contain references to other files which describe the contents of the individual pages, such other files including, for example, line art images, continuous tone images, text, fonts, etc. Each print sheet includes a recto side and a verso side. At least four pages are imposed on a single side of a print sheet, and some of these pages may be blank.
It should be noted that the words impositioning and impositioned are sometimes used for the words imposing and imposed, respectively.
Up to now, different proofing methods have been used to produce proofs of imposed documents from printing data produced by an imposition program. Known proofing methods produce flats, large sheets containing images for at least four pages in the resulting document. These flats have to be folded in a specific way, possibly after being combined with one or more other flats, and then cut to obtain a simulation of the document to be printed. Folding and cutting the flats is a very labor-intensive process.
Blueprint proofing methods start with film and make one copy of a printed sheet by a photo chemical process. The primary disadvantage of these methods is that they are expensive in consumption of consumables, due to the special paper and chemical products used. Additionally, in these methods, normally only one or two separations are transferred to the paper. By consequence, the resulting proofs cannot be used as a content proof for pages containing more than two separations, for example in four-color printing. Furthermore, these methods can only be used where film is the output of the prepress stage. Nowadays, the printing industry is shifting more and more towards computer-to-plate production, in which film is no longer used, and thus blueprint proofing can no longer be used.
Another prior art proofing method is the use of a short run proofing press. This is a small press which has a lower start up cost than a full scale printing press, the press on which the real printing stage of the document takes place. The proofing press is used to print only a small amount of examples. The same plates are used in the proofing press that are used on the printing press and therefore this method has the disadvantage that the format of the proofing press must be at least the format of the printing press. Furthermore, although smaller costs are to be foreseen for starting up a short run proofing press, a high initial investment is needed for such a press.
A third proofing method involves page proofing and imposition proofing separately. In this method the pages are proofed unscaled on an electronic proofing device. Then the imposed sheets are downscaled to form a "mechanical" proof which shows whether pages are aligned correctly. The imposition proof has to be folded and cut, which again is labor-intensive, although a larger proofer can produce larger imposed sheets that do not require downscaling. The two main disadvantages of this method is that two proofs must be made and checked separately and that a physical model of the document as it will be printed eventually is not available to show to the customer.
Thus, there is a need in the art for a method of simulating on a proofing medium the printed results of printing an imposed document, the method avoiding folding and cutting.
One of the problems of proofing is that there is a chance that the printed proof will not be printed with the same data (photographs, text, etc.) as the final printing output. This can come about, for example, by some of the images used being modified during the time between proofing and final printing. Thus there is a need in the art for mechanisms that aid checking for correct placement and for version control in proofing.